1. Field of the Invention
The present invention relates to a stator-core fixing structure for a rotating electric machine.
2. Description of the Related Art
With regard to a conventional rotating electric machine, a stator-core fixing structure has been proposed in which a flange for holding a stator core is provided in a ring member and the flange is screwed and fixed to a housing case (e.g., Patent Document 1).
In such a conventional stator-core fixing structure, a flange portion, which is the outer circumference, of a ring member, that radially protrudes, is formed and screwed to the housing case; therefore, the outer diameter of a portion that is screwed to the housing case increases necessarily; moreover, because a pedestal portion for screwing needs to be provided in the housing case, the thickness of the housing case increases and hence the overall weight of the apparatus also increases.
Furthermore, in the case where part of the housing case is covered with a cover member, a screwing portion needs to be provided in the cover member in such a way as to avoid a portion, of the housing case, at which the flange portion and the housing case are screwed to each other, thereby causing the outer diameter to increase or causing the structure to become complex.
After the flange portion and the housing case are screwed to each other, the rotor and the cover member are inserted and then the cover member is screwed and fixed to the housing case; however, it is required to make the respective centers of the rotor and the stator coincide with each other with respect to the housing case.
Accordingly, in order to secure a gap between the rotor and the stator, it is required to consider central-point displacement between the housing case and the ring member; therefore, as a result, the gap between the rotor and the stator is enlarged and hence the outer diameter of the rotating electric machine may increase.
As a means to cope with the enlargement of the outer diameter, a means is conceivable in which a single and the same screw is utilized for both fixing the flange portion of the ring member to the housing case and fixing the cover member to the housing case and the flange portion of the ring member, the housing case, and the cover member are integrally screwed to one another.
However, in the case of the structure in which the flange portion of the ring member, the housing case, and the cover member are integrally screwed to one another, it is required that in order to prevent external water or oil from intruding therein, liquid packing materials or gaskets need to be provided between the members, thereby causing the material costs to increase or causing the assembly to become complicated.
In the case where liquid packing materials or gaskets are provided, it is required that the flatness of the flange portion and the degree of parallelism between the top and bottom sides of the flange portion are accurately maintained; therefore, in many cases, cutting processing for the flange portion is required and hence the apparatus becomes expensive.
Moreover, when the rotating electric machine is assembled, the ring member holding the stator is inserted into the housing case and then the cover member to which the rotor is fixed and the housing case are coupled with each other; however, in the case of a permanent-magnet rotating electric machine, the stator and the rotor are attracted to each other by the magnetic force of a permanent magnet; therefore, the ring member may be attracted by the rotor and may travel. Therefore, because it is required to assemble the rotating electric machine while supporting the housing case and the ring member by a positioning mechanism or while limiting the travel of the ring member, the material cost may increase or the assembly plant and the assembly method may become complex and complicated.